Technical Field. The present invention relates to a frontal structure in a vehicle comprising a pair of laterally spaced beams, each comprising a sheet metal box element having greater length than both width and height, and a portion which is oriented in the longitudinal direction of the vehicle, as well as a sensor or means for sensing the retardation of the vehicle during a collision and, as a function thereof, changing the rigidity of the beam in its longitudinal direction.
Background Information. Box beams are used in a number of different applications in automobiles, for example, as the front side members in passenger car chassis, and are thus components whose design crucially affects the crash safety of the vehicle. In attempting to achieve high crash safety, it has always been striven for, by a controlled crash sequence, to force as far as possible the elements in the structure to be deformed in the most energy absorbing manner, which is progressive upsetting or crumpling. Less energy-absorbing reactions such as rotation, buckling or bending should thus be avoided.
Ideally, from a collision safety point of view, the volume represented by the front portion of the vehicle should consist of a large number of cells, each of which having a large energy-absorbing capacity, regardless of from which direction the vehicle is struck, but such solutions have not been applicable in mass production for a number of reasons.
Normally, the beam system in a vehicle is regarded as a passive security system where it is primarily the geometric shape of the box-shaped beams which, by virtue of their energy-absorbing capacity, determine the collision security. It is, however, known to arrange an xe2x80x9cactivexe2x80x9d beam system in a vehicle, i.e. a system where a collision triggers an activity which makes the beam system perform in a manner exceeding its normal mechanical limits. Such an active beam arrangement is known, e.g. by U.S. Pat. No. 4,050,537. Here, an explosive charge is used to change, in a collision, the cross section of a box beam in such a manner that its rigidity, and thus its energy-absorbing capacity, increases.
The purpose of the present invention is to develop a frontal structure with an active beam system making it possible to adapt deformation and energy-absorbing capacity to various collision situations.
This is achieved according to the invention by virtue of the fact that the beams are each coordinated with an individual retardation sensor, each disposed to send an individual retardation-dependent signal to a control unit, which is disposed to compare the signals and activate said means to change the rigidity of the beams depending on the difference between the signals from the retardation sensors.
The invention creates an active frontal structure where technology which is known per se is used in an entirely new manner, built on the idea of dimensioning the beams for a certain collision situation requiring a certain rigidity and changing the rigidity of the beams for collision situations in which another rigidity is desirable.
The invention is in particular directed to a frontal structure in which the rigidity of the 20 beams, which dictates the deformation sequence and the energy-absorbing capacity, can be adapted to a more or less symmetrical frontal collision and to a so-called offset collision, i.e. a collision with a vehicle or object which strikes essentially to one side of the longitudinal center-plane of the vehicle.
In one embodiment, the beams can be dimensioned for offset collision, requiring great rigidity, since the entire, or most, deformation energy must be absorbed by only one of the beams. In a symmetrical frontal collision, the deformation energy is distributed between the beams, and the optimum absorption is obtained in this case by reducing the rigidity of the beams.
The beams in the frontal structure are thus active. By studying the deformation of a passive beam after a collision, it is possible to determine where the transition occurred between upsetting or crumple-fold-formation and buckling of the entire beam, for example. By actively softening the beam in this area, for example with the aid of small pyrotechnical charges, the buckling can be avoided and the crumple-fold-formation distance can thus be extended over the softened area to the area behind it, which can be more rigid.
In another embodiment, the beams can be dimensioned with a cross-sectional profile which provides optimum rigidity during a symmetrical frontal collision, the means for changing the rigidity of the beams being disposed in an offset collision to increase the rigidity by changing the cross-sectional profile, as disclosed in U.S. Pat. No. 4,050,537.